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2.4.8.3 Guarded Probe Station Configurations
Within the probe station, guarded configurations begin with triaxial signal
connectors, which are part of the ZN50C-T, DC/RF cable configuration for probe arms.
1. The center pin carries the signal. It is connected internally to the center
conductor of the cryogenic, coaxial cable that is attached to the ceramic blade
signal conductor and probe tip.
2. The middle ring carries the guard voltage. It is connected to the outer conductor
of the cryogenic, coaxial cable that is attached to the ceramic blade
reference plane.
3. The outer shell is available for shielding the external cable. It is connected to the
vacuum chamber. The shield is not carried inside the vacuum chamber in this
configuration. The chamber itself provides shielding.
For best performance, the sample must be guarded in addition to the cables. There is
a potential leakage path through the sample substrate to a standard grounded
sample holder. The SH-1.25-C or SH-2.00-C coaxial sample holder is recommended
for guarding samples in the Model CRX-6.5K. The FT-BNC coaxial feedthrough is used
to bring the guard voltage into the chamber and to the sample holder. When the
experiment requires guarding and back side voltage biasing or additional ground
isolation, the SH-1.25-T or SH-2.00-T triaxial sample holder is required in the
Model CRX-6.5K (FIGURE 2-27). The triaxial sample holder offers two layers of
isolation between the sample and grounded sample cooling assembly. The FT-TRIAX
triaxial feedthrough is required to connect signals to the sample holder
(FIGURE 2-28).
The coaxial and triaxial sample holders are almost identical in appearance; however, the
difference is the number of electrical isolation layers, which cannot be seen from the
outside.
FIGURE 2-26
Triaxial
connector
FIGURE 2-27
Triaxial sample holder (SH-1.25-T)
